Reagent concentration, temperature, and residence time are known factors that drive chemical reactions. Combustion chemical vapor deposition (combustion CVD) processes are no different. The significance of these factors and their controlling process parameters has been well documented.
Combustion chemical vapor deposition (combustion CVD) is a relatively new technique for the growth of coatings. Combustion CVD is described, for example, in U.S. Pat. Nos. 5,652,021; 5,858,465; and 6,013,318, each of which is hereby incorporated herein by reference in its entirety.
Conventionally, in combustion CVD, precursors are dissolved in a flammable solvent and the solution is delivered to the burner where it is ignited to give a flame. Such precursors may be vapor or liquid and fed to a self-sustaining flame or used as the fuel source. It will be appreciated that when used with a self-sustaining flame, a solvent may or may not be required. A substrate is then passed under the flame to deposit a coating.
There are several advantages of combustion CVD over traditional pyrolytic deposition techniques (such as CVD, spray and sol-gel, etc.). One advantage is that the energy required for the deposition is provided by the flame. A benefit of this feature is that the substrate typically does not need to be heated to temperatures required to activate the conversion of the precursor to the deposited material (e.g., a metal oxide). Also, a curing step (typically required for spray and sol-gel techniques) typically is not required. Another advantage is that combustion CVD techniques do not necessarily require volatile precursors. If a solution of the precursor can be atomized/nebulized sufficiently (e.g., to produce droplets and/or particles of sufficiently small size), the atomized solution will behave essentially as a gas and can be transferred to the flame without requiring an appreciable vapor pressure from the precursor of interest.
Conventional combustion CVD processes involve passing a precursor material directly through the entire length of the flame by inserting it into the combustion gas stream prior to being combusted. In some conventional techniques, a precursor/solvent solution is used as the fuel source. The temperature and residence time profile experienced by the precursor is controlled by the combustion conditions and/or burner-to-substrate distance. Unfortunately, however, these control mechanisms can be fairly limited, depending on the particular application.
It will be appreciated that combustion deposition techniques may be used to deposit metal oxide coatings (e.g., singly-layer anti-reflective coatings) on glass substrates, for example, to alter the optical properties of the glass substrates (e.g., to increase visible transmission). To this end, conventional combustion deposition techniques were used by the inventor of the instant application to deposit a single layer anti-reflective (AR) film of silicon oxide (e.g., SiO2 or other suitable stoichiometry). The attempt sought to achieve an increase in light transmission in the visible spectrum (e.g., wavelengths of from about 400-700 nm) over clear float glass with an application of the film on one or both sides. The clear float glass used in connection with the description herein is a low-iron glass known as “Extra Clear,” which has a visible transmission typically in the range of 90.3% to about 91.0%. Of course, the examples described herein are not limited to this particular type of glass, or any glass with this particular visible transmission.
The combustion deposition development work was performed using a conventional linear burner with 465 holes even distributed in 3 rows over an area of 0.5 cm by 31 cm (155 holes per row). By way of example and without limitation, FIG. 1a shows a typical linear burner, and FIG. 1b is an enlarged view of the holes in the typical linear burner of FIG. 1a. As is conventional, the linear burner was fueled by a premixed combustion gas comprising propane and air. It is, of course, possible to use other combustion gases such as, for example, natural gas, butane, etc. The standard operating window for the linear burner involves air flow rates of between about 150 and 300 standard liters per minute (SLM), using air-to-propane ratios of about 15 to 25. Successful coatings require controlling the burner-to-lite distance to between about 10-50 mm when a linear burner is used.
Typical process conditions for successful films used a burner air flow of about 225 SLM, an air-to-propane ratio of about 19, four passes of the substrate across the burner, a burner-to-lite distance of 35 mm, and a glass substrate velocity of about 50 mm/sec.
FIG. 2 is a simplified view of an apparatus 200 including a linear burner used to carry out combustion deposition. A combustion gas 202 (e.g., a propane air combustion gas) is fed into the apparatus 200, as is a suitable precursor 204 (e.g., via insertion mechanism 206, examples of which are discussed in greater detail below). Precursor nebulization (208) and at least partial precursor evaporation (210) occur within the apparatus 200. The precursor could also have been delivered as a vapor reducing or even eliminating the need for nebulization The flame 18 may be thought of as including multiple areas. Such areas correspond to chemical reaction area 212 (e.g., where reduction, oxidation, and/or the like may occur), nucleation area 214, coagulation area 216, and agglomeration area 218. Of course, it will be appreciated that such example areas are not discrete and that one or more of the above processes may begin, continue, and/or end throughout one or more of the other areas.
Particulate matter begins forming within the flame 18 and moves downward towards the surface 26 of the substrate 22 to be coated, resulting in film growth 220. As will be appreciated from FIG. 2, the combusted material comprises non-vaporized material (e.g., particulate matter), which is also at least partially in particulate form when coming into contact with the substrate 22. To deposit the coating, the substrate 22 may be moved (e.g., in the direction of the velocity vector). Of course, it will be appreciated that the present invention is not limited to any particular velocity vector, and that other example embodiments may involve the use of multiple apparatuses 200 for coating different portions of the substrate 22, may involve moving a single apparatus 200 while keeping the substrate in a fixed position, etc. The flame 18 is about 10-50 mm from the surface 26 of the substrate 22 to be coated.
Unfortunately, the heat flux produced during combustion deposition creates a significant increase in substrate temperature. Also, heat is delivered to a smaller area (e.g., in comparison to the IR burners of certain example embodiments described below) causing much larger temperature gradients. Furthermore, the substrate temperature increases with smaller burner-to-lite distances and increasing numbers of passes. For example, using the process conditions identified above, the back side of the substrate was found to reach a temperature of 162° C. This equates to a linear estimate of temperature rate of rise of 71° C./burner/m/min.
The substrate temperature extremes and resultant thermal gradient experienced by the glass during deposition leads to stress changes in the glass. This phenomenon, in turn, has resulted in spontaneous glass fracture during coating, in post-coating cooling, and/or in subsequent deposition of the same film on the opposite side of the lite. Additionally, the glass experiences bowing, which ultimately leads to coating uniformity issues.
Thus, it will be appreciated that there is a need in the art for combustion deposition techniques that overcome one or more of these and/or other disadvantages, and/or improved techniques for depositing metal oxide coatings (single layer anti-reflective coatings) on glass substrates via combustion deposition.
Recently, efforts have focused on investigating alternative burner designs. These efforts have led to the exploration of infrared and non-linear (e.g., two dimensional) burners produced by Maxon Corporation. One example of an IR burner design is disclosed in co-pending and commonly assigned application Ser. No. 12/000,784, filed on Dec. 17, 2007, the entire contents of which is hereby incorporated herein by reference.
Some techniques use a combustion deposition device in which the precursor is delivered independent of the flame. This approach is described in, for example, U.S. Publication No. 2005/0061036, the entire contents of which is hereby incorporated herein by reference. However, these products appear to involve substantially different burner designs and also appear to be limited to the deposition of optical preforms. Current remote CCVD (R-CCVD) efforts, such as those performed by Innovent, for example, aim for greater control over reaction conditions by delivering the precursor externally to the flame. The proposed design of certain example embodiments (described in greater detail below) improves upon this approach by utilizing IR burner technology. This provides for a substantially less turbulent reaction zone, which may provide improved coating uniformity and repeatability. Within an IR burner, combustion takes place primarily within the body of the burner before the combustion gasses exit the refractory faceplate. Additionally, IR burners of the type described herein consume less fuel and deliver heat over a substantially more planar area than conventional linear “ribbon” burners. The substantially lower flow rate of combustion gases per unit area and refractory faceplate provide for substantially less turbulent conditions at the exit of the burner, which may provide for a more controllable reaction zone, leading to improved coating uniformity and deposition repeatability. Additionally, the refractory faceplate also serves as an upper bound for the precursor containing carrier gas that is inserted between the faceplate and the glass. This has the effect of controlling the turbulence of the gasses within the reaction zone leading to greater control. It may also be possible to “tune” the primary wavelengths of IR radiation emitted from the refractory faceplate to favor certain reaction conditions through control of the combustion conditions. Indeed, the IR energy emitted from the refractory faceplate may be sufficient to promote precursor reaction and film growth. Of course, the use of an IR burner also may carry some or all of the advantages described in application Ser. No. 12/000,784 (the entire contents of which is hereby incorporated herein by reference).
In certain example embodiments, a fuel gas and oxygen source are selected and mixed together to form a combustion gas mixture. At least a portion of the combustion gas mixture is used in forming the coating. A precursor is selected such that at least a portion of the combustion products form a coating with desired properties. The precursor is introduced into the combustion gas stream to form a reagent mixture. Using at least one infrared burner, at least a portion of the reagent mixture is reacted via combustion to form reaction products, with at least a portion of the reaction products comprising non-vaporized material.
In certain example embodiments, a method of applying a coating to a substrate using combustion deposition is provided. A substrate having at least one surface to be coated is provided. A reagent (and optionally, a carrier medium) is selected, and if a carrier medium is selected, the reagent and the carrier medium are mixed together to form a reagent mixture, with the reagent being selected such that at least a portion of the reagent forms the coating. A precursor to be combusted with the reagent (or reagent mixture) is introduced, with the precursor including silicon. Using at least one infrared burner, at least a portion of the reagent (or reagent mixture) and the precursor are combusted to form a combusted material. The substrate is provided in an area so that the substrate is heated sufficiently to allow the combusted material to form the coating, directly or indirectly, on the substrate. The deposited coating comprises silicon oxide. The coating increases visible transmission of the glass substrate by at least about 1.7%.
In certain example embodiments, a method of applying a coating to a substrate using combustion deposition is provided. A substrate having at least one surface to be coated is provided. A reagent (and optionally, a carrier medium) is selected, and if a carrier medium is selected, and the reagent and the carrier medium are mixed together to form a reagent mixture, with the reagent being selected such that at least a portion of the reagent forms the coating. A precursor to be combusted with the reagent (or reagent mixture) is introduced, with the precursor including silicon. Via IR radiation from an IR radiation source, the IR radiation having a wavelength of about 2.5-3.5 microns distributed substantially two-dimensionally, at least a portion of the reagent (or reagent mixture) and the precursor are combusted to form a combusted material, the combusted material comprising non-vaporized material. The glass substrate is provided in an area about 2-5 mm from IR radiation source so that the glass substrate is heated sufficiently to allow the combusted material to form the coating substantially uniformly, directly or indirectly, on the glass substrate. The coating is substantially uniform.
In certain example implementations, the substrate temperature is heated to a temperature lower than that of conventional CVD and/or a lower temperature flame is used to combust the material to be combusted. In certain example implementations, the coating may be applied in a substantially uniform manner (e.g., across two dimensions), as measured by variations in thickness of the coating (e.g., with variations not exceeding about ±10%) and/or variations in the visible transmission gain (e.g., with variations in either percent transmission or percent transmission gain not exceeding about ±0.5%).
In addition to these example embodiments, the inventor of the instant application also has been able to create a remote combustion deposition burner in which the precursor is delivered along with a carrier gas stream to the reaction zone external to the flame. In brief, a distribution device provided in connection with certain example burner configurations provides an at least initially substantially laminar flow of a gaseous stream comprising the precursor and the carrier gas, which ultimately is substantially uniform across the coat zone. Thus, certain example embodiments realize at least some the benefits of infrared (IR) burner deposition described herein, as well as advantages more specific to using remote combustion deposition techniques including, for example, reduced heat flux to the substrate, reduced fuel consumption, possible enhanced reaction control and ability to use moisture/oxygen sensitive precursors to deposit coatings (as precursor can be delivered in inert carrier gas), and/or the like.
In certain example embodiments of this invention, a remote combustion deposition system for use in combustion deposition depositing a coating on a substrate is provided. An infrared (IR) burner is configured to generate radiant energy in an area between the burner and the substrate. A delivery device is configured to provide a stream comprising a substantially vaporized precursor and a carrier gas from a location that is remote from the radiant energy generated by the IR burner. The delivery device is further configured to cause the stream to flow between the substrate and the IR burner. In operation, the stream is substantially laminar when exiting the delivery device and, in operation, the radiant energy is sufficient to cause the precursor in the stream to be combusted and to heat the substrate to allow at least a portion of the combusted precursor to form the coating, directly or indirectly, on the substrate.
In certain example embodiments, a method of forming a coating on a glass substrate using combustion deposition is provided. A glass substrate having at least one surface to be coated is provided. At least one infrared (IR) burner is provided. A substantially laminar flow of a gaseous stream comprising a precursor and a carrier gas is provided, with the stream at least initially being provided remote from the IR burner. The stream is caused to pass between the substrate and the at least one IR burner. Using the at least one IR burner, at least a portion of the precursor in the stream is combusted to form a combusted material, with the combusted material comprising non-vaporized material. The glass substrate is provided in an area so that the glass substrate is heated sufficiently to allow the combusted material to form the coating, directly or indirectly, on the glass substrate.
Certain example embodiments also relate to methods of making coated articles in accordance with these and/or other example implementations.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.